Apparatus for the production of short-wave electromagnetic radiation

ABSTRACT

Apparatus for the production of short-wave electromagnetic radiaion, especially in the x-ray and gamma-ray region, by means of the interaction between accelerated charged particles, especially electrons or positrons, and a crystal lattice, with a charged-particle source for the production of a beam of energetic charged particles and with a crystal arrangement which is so arranged in the path of the charged particle radiation beam that the charged particles traverse the crystal lattice of the crystal arrangement parallel to a predetermined lattice direction (&#34;channeling-condition&#34;). In order to produce an electromagnetic radiation beam with predetermined convergence or divergence, there are used a correspondingly convergent or divergent charged particle radiation beam (212) as well as a crystal arrangement (214) which is so bent that the channeling condition is at least approximately fulfilled for all charged particle paths in the crystal. (FIG. 1)

BACKGROUND OF THE INVENTION

The present invention starts from an apparatus for the production ofshort-wave electromagnetic radiation, especially in the x-ray andgamma-ray region, by means of the interaction between acceleratedcharged particles, especially electrons or positrons, and a crystallattice, with a charged-particle source for the production of a beam ofenergetic charged particles and with a crystal arrangement which is soarranged in the path of the charged particle radiation beam that thecharged particles traverse the crystal lattice of the crystalarrangement parallel to a predetermined lattice direction("channeling-condition").

Energetic charged particles, which impinge upon a suitable singlecrystal at an angle to a crystal plane or a crystal axis which issufficiently small, are moved in an oscillatory fashion lengthwise ofthe pertinent crystal direction along the crystal plane or crystal axis,respectively, (so-called channeling or canalization) and emit therewithelectromagnetic radiation in the forward direction, the energy whereoflies in the x-ray or gamma-radiation region, assuming corresponding massand energy of the incident charged particles (so-called channeling- orcanalization-radiation). For example, electrons with an energy between20 and 100 MeV produce x-rays with energies between about 20 and 200 keVin monocrystalline silicon.

In the usual apparatus for the production of canalization-radiation acharged particle radiation of the smallest possible divergence is used,which impinges upon a flat single crystal parallel to a selected crystalplane or crystal axis, respectively (Appl. Phys. Lett. 57 (27), Dec. 31,1990, 2956-2958).

In the known apparatus of the aforementioned type, therefore, the mostparallel charged particle radiation possible is used, and there arisesan essentially parallel beam of electromagnetic radiation. For manyapplications, however, appreciably convergent or divergent beams ofshortwave electromagnetic radiation are required. This creates problems,since no focusing optical elements, such as lenses, are available forshort-wave electromagnetic radiation.

SUMMARY OF THE INVENTION

The present invention is based upon the task of further developing anapparatus of the aforementioned type in such a way that with it anon-parallel, and thus convergent or divergent, beam of short-waveelectromagnetic radiation, especially in the x-ray and gamma-ray region,can be produced.

This task solved by means of an apparatus for the production ofshort-wave electromagnetic radiaion, especially in the x-ray andgamma-ray region, by means of the interaction between acceleratedcharged particles, especially electrons or positrons, and a crystallattice, with a charged-particle source for the production of a beam ofenergetic charged particles and with a crystal arrangement which is soarranged in the path of the charged particle radiation beam that thecharged particles traverse the crystal lattice of the crystalarrangement parallel to a predetermined lattice direction (latticeplane, lattice axis) ("channeling-condition"), which is characterized inthat the crystal arrangment is traversed by the charged particles in atleast one plane passing through the axis of the charged particleradiation beam in directions which essentially converge into apredetermined point, and in that the crystal arrangement is so arrangedin an arc about the predetermined point, that the channeling conditionis substantially fulfilled for all charged particle beam paths.

The apparatus according to the invention makes it possible to create anon-parallel beam of short-wave electromagnetic radiation, especially inthe x-ray and gamma-ray region, with predetermined convergent- ordivergent properties, since the convergence or divergence, respectively,of the short-wave electromagnetic radiation is determined by theconvergence or divergence, respectively, of the charged particleradiation beam which impinges on the crystal arrangement; and the lattercan easily be influenced by particle-optical means, especially electronlenses and the like, and also allows the creation of curvedsingle-crystal arrangments without great difficulties. Furtherdevelopments of the present apparatus make possible a modulation of theintensity, or of the convergence or divergence, respectively, of theelectromagnetic radiation beam.

In the arrangement according to FIG. 4, one can relatively simplyrealize also a crystal arrangement which is bent in two planes, like aspherical cap, which can be used in combination with a rotationallysymmetrically converging or diverging charged particle radiation beam.

By means of pulsed or oscillatory bending of the crystal or crystals,respectively, or of the crystal arrangement, or by means of pulsed oroscillatory rotation of the plane segments of the crystal arrangementaccording to FIG. 4, the intensity or convergence/divergence,respectively, of the short-wave radiation beam which is produced can bemodulated in time and/or in space, and, if need be, be synchronized withexternal measurement conditions and/or corresponding changes in theconvergence or divergence, respectively, of the charged particleradiation beam. As is shown schematically in FIG. 4, a parallel electronradiation beam 512 which is produced by an accelerator 520 can be madeconvergent in the plane of the drawing by an electron opticalcylindrical lens 513. The electron optical lens is an electromagneticlens, which is supplied with current by a current-supply apparatus 515via a modulator 517. The modulator 517 allows one to control the currentstrength, and thereby the angle of convergence of the electron radiationbeam 512.

The single crystal segments 514a, 514b, . . . are mounted oncorresponding placement apparatus 519, so that the radius of curvatureof the crystal arrangement 514 can be altered. As FIG. 4a shows, theplacement apparatus can at any given time include a control curve 519a,lengthwise of which the pertinent crystal segment 514c is displaced andswiveled.

Instead of a cylindrically curved crystal, one can also use aspherically curved crystal, with sufficiently small crystal-size andcrystal-thickness. In combination with a rotationally symmetric,convergent or divergent charged particle radiation beam, one can thenfulfil the channeling-condition in a rotationally symmetric manner for aspecial crystal axis. Of course, corresponding considerations applyquite generally for crystals which are curved in two directions, e.g. inellipsoidal form.

The angle of convergence or divergence, respectively, of the chargedparticle radiation beam will in general be greater than 0.1 mrad, e.g.greater than 0.3 mrad. As a monocrystalline crystal material, one canuse e.g. silicon or diamond. As charged particles electrons arepreferred, whose energies amount in general to above 1 MeV, preferablyabove 10 MeV. Suitable crystal directions are e.g. the [111] axis andthe [100] plane in the case of silicon, and the [110] axis in the caseof diamond. The thickness of the crystal arrangement can lie betweenabout 1 μm and 1 mm. The materials and values which are given arenon-limiting examples.

It has proven advantageous to cool the crystal or the crystals,respectively, e.g. by means of liquid nitrogen. In this way theline-heights of the electromagnetic radiation which is produced may beenlarged and their line-width reduced. The crystal arrangement can, forthis purpose, be arranged in a suitable cryostat 224, as shownschematically in FIG. 1.

Hereinafter examples of embodiments of the invention will be explainedin greater detail with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a horizontal section of an embodiment of the apparatusaccording to the invention for the production of a convergent beam ofshort-wave electromagnetic radiation;

FIG. 2 shows a vertical section of a further embodiment of the inventionfor the production of a convergent beam of short-wave electromagneticradiation;

FIG. 3 shows a horizontal section of an embodiment of an apparatusaccording to the invention for the production of a divergent beam ofshort-wave electromagnetic radiation,

FIGS. 4 and 4a show a horizontal section of a further embodiment of theinvention for the production of a convergent beam of short-waveelectromagnetic radiation,

FIG. 5 shows a schematic representation of a known apparatus for theproduction of short-wave electromagnetic radiation by means ofchanneling;

DETAILED DESCRIPTION

FIG. 5 shows a channeling- or canalization-apparatus of customaryconstruction in top view. A completely parallel charged-particle beam12, produced by a charged-particle source 10 represented onlyschematically, e.g. an accelerator, impinges on a flat crystal 14. Thecharged particles, e.g. electrons, are moved along a predeterminedlattice direction, thus parallel to a predetermined lattice plane orlattice axis, through the crystal and produce there, by interaction withthe crystal lattice, an essentially parallel beam 26 of short-waveelectromagnetic radiation, e.g. in the gamma ray region. The radiationis in general linearly polarized by the planar channeling. The chargedparticles which have passed through the crystal 14 are deflected away bya deflecting magnet 18 out of the beam path of the gamma radiation beam16 and then impinge on a catcher not shown in FIG. 5. In this knownapparatus the charged particle beam 12 as well as the gamma ray beam 16are essentially parallel in a horizontal and in a vertical plane.

In the embodiment of the invention shown in FIG. 1 the charged particlesource (not shown) delivers a charged particle radiation beam (inparticular an electron radiation beam) 212 which is convergent in theplane of the drawing and substantially parallel in the planeperpendicular thereto. The electron radiation source can include e.g. acylindrical electron lens. A platelet-shaped single crystal 214 isarranged in the path of the electron radiation beam 212, said crystal214 being curved cylindrically about an axis running perpendicular tothe plane of the drawing (The bending of the crystal is greatlyexaggerated as shown in FIG. 1 as well as in FIGS. 3 and 4 for the sakeof clarity). Thus in the plane of the drawing the directions of theelectron radiation paths in the crystal converge in a predeterminedpoint 220, and the crystal is cylindrically curved in such a manner thatthe channeling- or canalization-condition is substantially fulfilled forall charged particle radiation paths in the curved crystal 214. Thex-ray- or gamma-radiation which is emitted from the crystal in theforward direction of the electron radiation thus likewise converges inthe plane of the drawing and in planes parallel to this, so that aline-focus arises at the axis of the bending. The cylindricallysymmetrically converging electron radiation beam is deflected by adeflecting magnet 218 after it has passed through the crystal 214 andimpinges into a catcher 222. The bending axis of the crystal 214 thusruns through the point 220 in the plane of the drawing.

In the embodiment shown in FIG. 2, which is shown as a section planeperpendicular to FIG. 1, the charged particle radiation beam 312 whichis produced by the charged particle source is convergent in two mutuallyperpendicular planes (i.e. in the plane of the drawing and in the planewhich is perpendicular to this) and produces, in combination with thecrystal 314, which is cylindrically bent with respect to an axis 319lying in the plane of the drawing, a point focus at the point 320, sincethe channeling condition is substantially fulfilled in all planes of thecylindrically bent crystal which pass through the axis 319 (includingthe plane of the drawing). The deflecting magnet and the catcher, whichare usually provided in an apparatus of the present type, are not shownin FIG. 2 and the following Figures.

In the embodiment according to FIG. 3 the charged particle source (notshown) delivers a divergent charged particle radiation beam 412. Thecrystal 414 is correspondingly bent concavely, cylindrically orrotationally symmetrical with respect to the charged particle beamsource, so that the crystal directions (crystal planes, crystal axes)along which the channeling takes place run at any given time parallel tothe individual charge particle ray path. The convergence point 420 ofthe charged particle beam directions in the crystal and of the chosencrystal directions thus lies in FIG. 3 on the side of the crystal whichfaces the charged particle source and not on the side facing away fromthe charged particle source as in the case of the crystal in FIGS. 1 and2.

In the embodiment shown in FIG. 4 the impinging charged particleradiation beam 512 is again convergent in one or two planes orrotationally symmetrically. Here as crystal arrangement one does not usea single, correspondingly curved single crystal, but rather a pluralityof curved or in some cases even plane monocrystalline-platelets or-segments 514a, 514b, . . . which are arranged in an arc or a sphericalsurface about the convergence point 520. If the segments 514a, . . . aresufficiently small, they can consist of flat monocrystalline pieces.Moreover, it is obviously simpler to bend smaller crystal platelets thana large monocrystalline plate.

I claim:
 1. Apparatus for the production of short-wave electromagneticradiaion, especially in the x-ray and gamma-ray region, by means of theinteraction between accelerated charged particles, especially electronsor positrons, and a crystal lattice, with a charged-particle source forthe production of a beam (212, 312, 412, 512) of energetic chargedparticles and with a crystal arrangement (214, 314, 414, 514) which isso arranged in the path of the charged particle radiation beam that thecharged particles traverse the crystal lattice of the crystalarrangement parallel to a predetermined lattice direction (latticeplane, lattice axis) ("channeling-condition"), comprising in combinationa crystal arrangment (214, 314, 414, 514) and means for directingcharged particles through said crystal arrangement in at least one planepassing through the axis of the charged particle radiation beam (212,312, 412, 512) in directions which essentially converge into apredetermined point (220, 320, 520), said crystal arrangement having aside facing away from said charged particle source and a side facingtoward said charged particle source, said crystal arrangement being soarranged in an arc about the predetermined point, that the channelingcondition is substantially fulfilled for all charged particle beampaths.
 2. Apparatus according to claim 1, wherein said means fordirecting charged particles includes means for directing said chargedparticles in such a manner that the charged particle radiation beamwhich impinges on the crystal arrangement (214, 314, 514) is convergentand that the predetermined point (220, 320, 520) lies on the side of thecrystal arrangement which faces away from the charged particle source.3. Apparatus according to claim 2, wherein said means for directingcharged particles includes means for directing said charged particles insuch a manner that the charged particle radiation beam which impinges onthe crystal arrangement (214, 314, 514) is convergent in two mutuallyperpendicular planes.
 4. Apparatus according to claim 1, characterizedin that the charged particle radiation beam which impinges on thecrystal arrangement (414) is divergent and in that the predeterminedpoint (220, 320, 520) lies on the side of the crystal arrangement whichfaces the charged particle source.
 5. Apparatus according to any one ofclaims 1 through 4, characterized in that the crystal arrangementconsists of one curved single crystal.
 6. Apparatus according to claim5, characterized in that the single crystal is cylindrically curved. 7.Apparatus according to any one of claims 1 through 4, characterized inthat the crystal arrangement consists of several segments (514a, 514b, .. . ).
 8. Apparatus according to claim 7, characterized in that thesegments consist of curved monocrystalline platelets.
 9. Apparatusaccording to claim 7, characterized in that the segments consist of flatmonocrystalline platelets.
 10. Apparatus according to any one of claims1 through 4 characterized by an apparatus for changing the bending ofthe crystal apparatus.
 11. Apparatus according to claim 7, characterizedby an apparatus for swiveling the segments of the crystal arrangement.12. Apparatus according to claim 2 characterized by an apparatus forchanging the convergence of the charged particle radiation beam. 13.Apparatus according to claim 12, characterized by a synchronization ofthe or convergence-changing apparatus with a bend-changing apparatus ora turning apparatus, respectively.
 14. Apparatus according to claim 1,characterized by an apparatus for cooling the crystal arrangement. 15.Apparatus according to claim 4, characterized by an apparatus forchanging the divergence of the charged particle radiation beam. 16.Apparatus according to claim 15, characterized by a synchronization ofthe divergence-changing apparatus with a bend-changing apparatus or aturning apparatus, respectively.